Cellular Respiration Harvesting Chemical Energy

AP Biology 2006-2007

Cellular RespirationHarvesting Chemical Energy

ATP


What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

Harvesting stored energy Energy is stored in organic molecules

carbohydrates, fats, proteins Heterotrophs eat these organic molecules food

digest organic molecules to get… raw materials for synthesis fuels for energy

controlled release of energy “burning” fuels in a series of

step-by-step enzyme-controlled reactions

AP Biology

Harvesting stored energy Glucose is the model

catabolism of glucose to produce ATP

C6H12O6 6O2 ATP 6H2O 6CO2+ + +

CO2 + H2O + heatfuel

(carbohydrates)

COMBUSTION = making a lot of heat energy by burning fuels in one step

RESPIRATION = making ATP (& some heat)by burning fuels in many small steps

CO2 + H2O + ATP (+ heat)

ATPglucose

glucose + oxygen energy + water + carbondioxide

res

pir

ati

on

O2 O2

+ heat

enzymesATP

AP Biology

How do we harvest energy from fuels? Digest large molecules into smaller ones

break bonds & move electrons from one molecule to another as electrons move they “carry energy” with them that energy is stored in another bond,

released as heat or harvested to make ATP

e-

+ +e-

+ –loses e- gains e- oxidized reduced

oxidation reduction

redox

e-

AP Biology

How do we move electrons in biology? Moving electrons in living systems

electrons cannot move alone in cells electrons move as part of H atom move H = move electrons

pe

+

H

+H

+ –loses e- gains e- oxidized reduced

oxidation reduction

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reductionHe-

AP Biology

Coupling oxidation & reduction REDOX reactions in respiration

release energy as breakdown organic molecules break C-C bonds strip off electrons from C-H bonds by removing H atoms

C6H12O6 CO2 = the fuel has been oxidized electrons attracted to more electronegative atoms

in biology, the most electronegative atom? O2 H2O = oxygen has been reduced

couple REDOX reactions & use the released energy to synthesize ATP

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

O

2

AP Biology

Oxidation & reduction Oxidation

adding O removing H loss of electrons releases energy exergonic

Reduction removing O adding H gain of electrons stores energy endergonic

C6H12O6 6O2 6CO2 6H2O ATP+ + +

oxidation

reduction

AP Biology

Moving electrons in respiration Electron carriers move electrons by

shuttling H atoms around NAD+ NADH (reduced) FAD+2 FADH2 (reduced)

+ Hreduction

oxidation

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

H

adenine

ribose sugar

phosphates

NAD+

nicotinamideVitamin B3niacin

PO–

O–

O

–O

PO–

O–

O

–O

CC

O

NH2

N+

HNADH

carries electrons as a reduced molecule

reducing power!

How efficient!Build once,

use many ways

H

like $$in the bank

AP Biology

Overview of cellular respiration 4 metabolic stages

Anaerobic respiration1. Glycolysis

respiration without O2

in cytosol

Aerobic respiration respiration using O2

in mitochondria

2. Pyruvate oxidation

3. Krebs cycle

4. Electron transport chain

C6H12O6 6O2 ATP 6H2O 6CO2+ + + (+ heat)


What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

ATP synthase enzyme H+ flows through it

conformational changes

bond Pi to ADP to make ATP

set up a H+ gradient allow the H+ to flow

down concentration gradient through ATP synthase

ADP + Pi ATPH+

H+H+

H+

H+ H+

H+H+H+

ATP

ADP P+

But… How is the proton (H+) gradient formed?

And how do we do that?

AP Biology 2006-2007H+

H+H+

H+

H+ H+

H+H+H+

ATP

Got to wait untilthe sequel!

Got the Energy? Ask Questions!

ADP P+


Cellular RespirationStage 1:

Glycolysis


What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

Glycolysis

glucose pyruvate2x6C 3C

In thecytosol?

Why doesthat make

evolutionarysense?

That’s not enoughATP for me!

Breaking down glucose “glyco – lysis” (splitting sugar)

ancient pathway which harvests energy but it’s inefficient

generate only 2 ATP for every 1 glucose occurs in cytosol

AP Biology

Evolutionary perspective Prokaryotes

first cells had no organelles Anaerobic atmosphere

life on Earth first evolved without free oxygen (O2) in atmosphere

energy had to be captured from organic molecules in absence of O2

Prokaryotes that evolved glycolysis are ancestors of all modern life ALL cells still utilize glycolysis

Enzymesof glycolysis are“well-conserved”

AP Biology

10 reactions convert

glucose (6C) to 2 pyruvate (3C)

produces: 4 ATP & 2 NADH

consumes:2 ATP

net yield: 2 ATP & 2 NADH

glucoseC-C-C-C-C-C

fructose-1,6bPP-C-C-C-C-C-C-P

DHAPP-C-C-C

G3PC-C-C-P

pyruvateC-C-C

Overview

DHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate

ATP2

ADP2

ATP4

ADP4

NAD+2

2Pi

enzyme

enzyme

enzyme enzyme

enzyme

enzyme

enzyme

enzyme

2Pi

2H2

AP Biology

Glycolysis summary endergonicinvest some ATP

exergonicharvest a little ATP & a little NADH

net yield2 ATP2 NADH

4 ATP

ENERGY INVESTMENT

ENERGY PAYOFF

G3PC-C-C-P

NET YIELD

like $$in the bank

-2 ATP

AP Biology

Pi

3

6

4,5

ADP

NAD+

Glucose

hexokinase

phosphoglucoseisomerase

phosphofructokinase

Glyceraldehyde 3-phosphate (G3P)

Dihydroxyacetonephosphate

Glucose 6-phosphate

Fructose 6-phosphate

Fructose 1,6-bisphosphate

isomerase

glyceraldehyde3-phosphate

dehydrogenase

aldolase

1,3-Bisphosphoglycerate(BPG)

1,3-Bisphosphoglycerate

(BPG)

1

2

ATP

ADP

ATP

NADH

NAD+

NADH

Pi

CH2

C O

CH2OH

P O

CH2 O P

O

CHOH

C

CH2 O P

O

CHOH

CH2 O PO

CH2OP

O

PO

CH2

H

CH2OHO

CH2 POO

CH2OH

P O

1st half of glycolysis (5 reactions)

Glucose “priming”

get glucose ready to split phosphorylate

glucose molecular

rearrangement split destabilized

glucose

AP Biology

2nd half of glycolysis (5 reactions)

Payola!Finally some

ATP!

7

8

H2O9

10

ADP

ATP

3-Phosphoglycerate(3PG)




Phosphoenolpyruvate(PEP)


Pyruvate Pyruvate

phosphoglyceratekinase

phosphoglycero-mutase

enolase

pyruvate kinase

ADP

ATP

ADP

ATP

ADP

ATP

H2O

CH2OH

CH3

CH2

O-

O

C

PH

CHOH

O-

O-

O-

C

C

C

C

C

C

P

P

O

O

O

O

O

O

CH2

NAD+

NADH

NAD+

NADH

Energy Harvest G3P

C-C-C-PPiPi 6

DHAPP-C-C-C

NADH production G3P donates H oxidizes the sugar reduces NAD+

NAD+ NADH ATP production

G3P pyruvate PEP sugar donates P

“substrate level phosphorylation”

ADP ATP

AP Biology

Substrate-level Phosphorylation

P is transferred from PEP to ADPkinase enzymeADP ATP

I get it!The Pi camedirectly from

the substrate!

H2O9

10



Pyruvate Pyruvate

enolase

pyruvate kinaseADP

ATP

ADP

ATP

H2O

CH3

O-

O

C

O-

C

C

C

P

O

O

O

CH2

In the last steps of glycolysis, where did the P come from to make ATP? the sugar substrate (PEP)

ATP

AP Biology

Energy accounting of glycolysis

Net gain = 2 ATP + 2 NADH some energy investment (-2 ATP) small energy return (4 ATP + 2 NADH)

1 6C sugar 2 3C sugars

2 ATP 2 ADP

4 ADP

glucose pyruvate2x6C 3C

All that work! And that’s all

I get?

ATP4

2 NAD+ 2 Butglucose has

so much moreto give!

AP Biology

Is that all there is? Not a lot of energy…

for 1 billon years+ this is how life on Earth survived no O2 = slow growth, slow reproduction

only harvest 3.5% of energy stored in glucose more carbons to strip off = more energy to harvest

Hard wayto makea living!

O2

O2

O2

O2

O2

glucose pyruvate6C 2x 3C

AP Biology

7

8

H2O9

10

ADP

ATP







Pyruvate Pyruvate

ADP

ATP

ADP

ATP

ADP

ATP

H2O

NAD+

NADH

NAD+

NADH

PiPi 6

Glycolysisglucose + 2ADP + 2Pi + 2 NAD+ 2 pyruvate + 2ATP + 2NADH

But can’t stop there!

Going to run out of NAD+

without regenerating NAD+, energy production would stop!

another molecule must accept H from NADH so NAD+ is freed up for another round

PiNAD+

G3P

1,3-BPG 1,3-BPG

NADH

NAD+

NADH

Pi

DHAP

raw materials products

AP Biology

NADH

pyruvate

acetyl-CoA

lactate

ethanol

NAD+

NAD+

NADH

NAD+

NADH

CO2

acetaldehyde

H2O

Krebscycle

O2

lactic acidfermentation

with oxygenaerobic respiration

without oxygenanaerobic respiration

“fermentation”

How is NADH recycled to NAD+?Another molecule must accept H from NADH

recycleNADH

which path you use depends on who you are…

which path you use depends on who you are…

alcoholfermentation

AP Biology

Fermentation (anaerobic) Bacteria, yeast

1C3C 2Cpyruvate ethanol + CO2

Animals, some fungi

pyruvate lactic acid3C 3C

beer, wine, bread

cheese, anaerobic exercise (no O2)

NADH NAD+

NADH NAD+

back to glycolysis

back to glycolysis

AP Biology

recycleNADH

Alcohol Fermentation

1C3C 2Cpyruvate ethanol + CO2

NADH NAD+

Count thecarbons!

Dead end process at ~12% ethanol,

kills yeast can’t reverse the

reaction

bacteria yeast

back to glycolysis

AP Biology

recycleNADH

Reversible process once O2 is available,

lactate is converted back to pyruvate by the liver

Lactic Acid Fermentationpyruvate lactic acid

3C 3CNADH NAD+

Count thecarbons!

O2

animalssome fungi

back to glycolysis

AP Biology

Pyruvate is a branching pointPyruvate

O2O2

mitochondriaKrebs cycle

aerobic respiration

fermentationanaerobicrespiration


What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

H+

H+H+

H+

H+ H+

H+H+H+


ATP

But… Have we done that yet?

ADP P+

ATP synthase set up a H+ gradient allow H+ to flow

through ATP synthase powers bonding

of Pi to ADP

ADP + Pi ATP


NO!There’s still more to my

story!Any Questions?


Cellular RespirationStage 2 & 3:

Oxidation of PyruvateKrebs Cycle

AP Biology

pyruvate CO2

Glycolysis is only the start Glycolysis

Pyruvate has more energy to yield 3 more C to strip off (to oxidize) if O2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full

oxidation of sugar to CO2

2x6C 3Cglucose pyruvate

3C 1C

AP Biology

Cellular respiration

AP Biology

intermembranespace inner

membrane

outermembrane

matrix

cristae

Mitochondria — Structure Double membrane energy harvesting organelle

smooth outer membrane highly folded inner membrane

cristae intermembrane space

fluid-filled space between membranes matrix

inner fluid-filled space DNA, ribosomes enzymes

free in matrix & membrane-bound

mitochondrialDNA

What cells would have a lot of mitochondria?

AP Biology

Mitochondria – Function

What does this tell us about the evolution of eukaryotes?

Endosymbiosis!

Dividing mitochondriaWho else divides like that?

Advantage of highly folded inner membrane?More surface area for membrane-bound enzymes & permeases

Membrane-bound proteinsEnzymes & permeases

Oooooh!Form fits function!

bacteria!

AP Biology

pyruvate acetyl CoA + CO2

Oxidation of pyruvate

NAD

3C 2C 1C[2x ] Pyruvate enters mitochondrial matrix

3 step oxidation process releases 2 CO2 (count the carbons!)

reduces 2 NAD 2 NADH (moves e-) produces 2 acetyl CoA

Acetyl CoA enters Krebs cycle

Wheredoes theCO2 go?Exhale!

AP Biology

Pyruvate oxidized to Acetyl CoA

Yield = 2C sugar + NADH + CO2

reduction

oxidation

Coenzyme APyruvate

Acetyl CoA

C-C-CC-CCO2

NAD+

2 x [ ]

AP Biology

Krebs cycle

aka Citric Acid Cycle in mitochondrial matrix 8 step pathway

each catalyzed by specific enzyme step-wise catabolism of 6C citrate molecule

Evolved later than glycolysis does that make evolutionary sense?

bacteria 3.5 billion years ago (glycolysis) free O2 2.7 billion years ago (photosynthesis)

eukaryotes 1.5 billion years ago (aerobic respiration = organelles mitochondria)

1937 | 1953

Hans Krebs1900-1981

AP Biology

4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the carbons!

3Cpyruvate

x2

oxidationof sugars

This happens twice for each glucose molecule

AP Biology

4C

6C

4C

4C

4C

2C

6C

5C

4C

CO2

CO2

citrate

acetyl CoACount the electron carriers!

3Cpyruvate

reductionof electron

carriers

This happens twice for each glucose molecule x2

CO2

NADH

NADH

NADH

NADH

FADH2

ATP

AP Biology

So we fully oxidized glucose

C6H12O6

CO2

& ended up with 4 ATP!

Whassup?

What’s the point?

AP Biology

Krebs cycle produces large quantities of electron carriers NADH FADH2

go to Electron Transport Chain!

Electron Carriers = Hydrogen Carriers

What’s so important about

electron carriers?

H+

H+H+

H+

H+ H+

H+H+H+

ATP

ADP+ Pi

AP Biology

Energy accounting of Krebs cycle

Net gain = 2 ATP

= 8 NADH + 2 FADH2

1 ADP 1 ATPATP

2x

4 NAD + 1 FAD 4 NADH + 1 FADH2

pyruvate CO2

3C 3x 1C

AP Biology

Value of Krebs cycle? If the yield is only 2 ATP then how was the

Krebs cycle an adaptation? value of NADH & FADH2

electron carriers & H carriers reduced molecules move electrons reduced molecules move H+ ions

to be used in the Electron Transport Chain

like $$in the bank


What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

H+

H+H+

H+

H+ H+

H+H+H+


ATP

But… Have we done that yet?

ADP P+

ATP synthase set up a H+ gradient allow H+ to flow

through ATP synthase powers bonding

of Pi to ADP

ADP + Pi ATP


NO!The final

chapter to my story is next!

Any Questions?


Cellular RespirationStage 4:

Electron Transport Chain

AP Biology



What’s thepoint?

The pointis to make

ATP!

ATP

AP Biology

ATP accounting so far… Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need to

extract more energy than 4 ATP!

A working muscle recycles over 10 million ATPs per second

There’s got to be a better way!

I need a lotmore ATP!

AP Biology

There is a better way! Electron Transport Chain

series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes

transport of electrons down ETC linked to pumping of H+ to create H+ gradient

yields ~36 ATP from 1 glucose! only in presence of O2 (aerobic respiration)

O2That

sounds morelike it!

AP Biology

Mitochondria Double membrane

outer membrane inner membrane

highly folded cristae enzymes & transport

proteins intermembrane space

fluid-filled space between membranes

Oooooh!Form fits function!

AP Biology


Intermembrane space

Mitochondrial matrix

Q

C

NADH dehydrogenase

cytochromebc complex

cytochrome coxidase complex

Innermitochondrialmembrane

AP Biology

G3PGlycolysis Krebs cycle

8 NADH2 FADH2

Remember the Electron Carriers?

2 NADH

Time tobreak open

the piggybank!

glucose

AP Biology


intermembranespace

mitochondrialmatrix

innermitochondrialmembrane

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–

FADH2

12

NADH dehydrogenase

cytochromebc complex


FAD

e–

H

H e- + H+

NADH NAD+ + H

H

pe

Building proton gradient!

What powers the proton (H+) pumps?…

AP Biology H+

H+H+

H+

H+ H+

H+H+H+

ATP

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–FADH2

12

NADH dehydrogenase

cytochrome bc complex


FAD

e–

Stripping H from Electron Carriers Electron carriers pass electrons & H+ to ETC

H cleaved off NADH & FADH2

electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in

mitochondrial membrane (ETC) flowing electrons = energy to do work

transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space

ADP+ Pi

TA-DA!!Moving electrons

do the work!

H+ H+ H+

AP Biology

But what “pulls” the electrons down the ETC?

electronsflow downhill

to O2 oxidative phosphorylation

O2

H2O

AP Biology

Electrons flow downhill Electrons move in steps from

carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy

make ATPinstead of

fire!

AP BiologyH+

ADP + Pi

H+H+

H+

H+ H+

H+H+H+We did it!

ATP

Set up a H+

gradient Allow the protons

to flow through ATP synthase

Synthesizes ATP

ADP + Pi ATP

Are wethere yet?

“proton-motive” force

AP Biology

The diffusion of ions across a membrane build up of proton gradient just so H+ could flow

through ATP synthase enzyme to build ATP

Chemiosmosis

Chemiosmosis links the Electron Transport Chain to ATP synthesis

Chemiosmosis links the Electron Transport Chain to ATP synthesis

So that’sthe point!

AP Biology

Peter Mitchell Proposed chemiosmotic hypothesis

revolutionary idea at the time

1961 | 1978

1920-1992

proton motive force

AP Biology

H+

H+

O2+

Q C

ATP

Pyruvate fromcytoplasm

Electrontransportsystem

ATPsynthase

H2O

CO2

Krebscycle

Intermembranespace

Innermitochondrialmembrane

1. Electrons are harvested and carried to the transport system.

2. Electrons provide energy

to pump protons across the membrane.

3. Oxygen joins with protons to form water.

2H+

NADH

NADH

Acetyl-CoA

FADH2

ATP

4. Protons diffuse back indown their concentrationgradient, driving the synthesis of ATP.

Mitochondrial matrix

21

H+

H+

O2

H+

e-

e-

e-

e-

ATP

AP Biology


2 ATP 2 ATP ~36 ATP+ +

~40 ATP

AP Biology

Summary of cellular respiration

Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed

in this equation? Why do we breathe?

C6H12O6 6O2 6CO2 6H2O ~40 ATP+ + +

AP Biology

ETC backs up nothing to pull electrons down chain NADH & FADH2 can’t unload H

ATP production ceases cells run out of energy and you die!

Taking it beyond… What is the final electron acceptor in

Electron Transport Chain?

O2

So what happens if O2 unavailable?

NAD+

Q

C

NADH H2O

H+

e–

2H+ + O2

H+H+

e–FADH2

12

NADH dehydrogenase

cytochrome bc complex


FAD

e–


What’s thepoint?

The pointis to make

ATP!

ATP

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Cellular Respiration Harvesting Chemical Energy